Apparatus for controlling warp knitting latch needles

ABSTRACT

Warp knitting operations of latch needles are controlled in accordance with a program representing a pattern by electromagnets acting on resilient armature portions of the latches so that coupling portions only of selected latches are placed in the path of reciprocating control means for being raised to cooperate with raised hooks of the latch needles. The present invention is concerned with a warp knitting or like machine. The machine is in some respects similar to a standard Raschel machine, but is provided with latch needles including a tubular hook part, and a latch part slidable in the tubular hook part.

PATENTEMM 14 m2 3 702 547 SHEET 2 BF 3 MHZ/M51 J JTRIKDQ ATTORNEY PATENTEDunv 14 m2 3. 702.547

SHEEI 3 [IF 3 f?" INVENTOR h/GMEL 3. NRA ER ATTORNEY APPARATUS FOR CONTROLLING WARP KNITTING LATCH NEEDLES BACKGROUND OF THE INVENTION The present invention is concerned with a machine in which, due to controlled relative movement between the hook part and the latch part of each latch needle, the hooks are alternately closed by the latches and opened again while cooperating with lapping guides which insert the warp threads into the open hooks so that a warp knitted fabric is formed.

in order to produce any desired optional pattern on a warp knitting machine, arrangements have been provided for controlling the individual latches independently of each other.

For example, the British Pat. No. 1, 192,129 discloses an apparatus provided with a carrier for raising latch parts having extensions. The engagement of each of which with the carrier in the raised position of the latter is controlled in accordance with the program by respective selecting electromagnets. The carrier is constituted by the bed reciprocating in the direction of the knitting needles, in which bed the elastic needles are arranged to be displaced perpendicularly to the direction of the bed motion to two end positions, one of which is the operative engaging position, and the other an inoperative position. The advance of the elastic needles in the bed, and consequently their engagement with the extensions of the latch part, is controlled by the armatures of the selecting electromagnets. Depending on whether the respective electromagnet is energized or not energized, the elastic needle engages the extension of the latch, and the carrier lifts the latch, or the elastic needle remains inoperative, and out of engagement with the extension so that irrespective of the rise of the carrier, the latch remains in its lower position. Consequently, during the rising of the carrier, the hooks of some selected needles can be closed by the latches according to the program in the uppermost position of the hook parts of the needles, whereas the hooks of other selected needles are closed in the knock-over intennediate position of the needles, and the hook of the remaining needles are closed in the lowermost position only.

The first-mentioned group of needles is inoperative during this phase, since their hooks are closed while the thread is laid into the other needles, whereas the second needle group knits a normal knitting pattern, and the stitch formed on the needles of the third group in the preceding course is not knocked-over from the needle, but remains in the hook, and the thread laid therein forms a blind loop. The advancing of the elastic needles toward the selecting electromagnets requires a special device, which is complicated so that the manufacture thereof is difficult and expensive.

SUMMARY OF THE INVENTION It is one object of the invention to improve the known apparatus for controlling latch needles operated in a warp knitting machine, and to provide simple and inexpensive structure for obtaining control of the needles in accordance with a program.

Another object of the invention is to provide the latches of latch needles with resilient control portions which form the armatures of selecting electromagnets.

Another object of the invention is to couple latches selected by the selector magnets, with reciprocating control means for raising the latches in accordance with the positions of their respective hooks.

With these objects in view, the present invention provides resilient latch extensions controlled by selecting electromagnets in order to control the engagement of the reciprocating control means with each individual extension in accordance with a program. it is a particularly novel feature of the invention, that the extensions of the latches constitute resilient armatures of the selecting electromagnets, and are provided with at least one coupling portion for engaging the reciprocating control means, such as a control bar.

An embodiment of the invention comprises a set of electromagnets selectively energizable in accordance with a program; a set of latch needle means, each including a hook, and a latch including a resilient control portion having at least one coupling portion, the resilient control portions forming the armatures of the electromagnets, respectively, and being movable by the same between an untensioned control position, and a tensioned control position attracted by the respective electromagnet; first operating means for advancing and retracting the hooks; and second operating means including at least one reciprocating control means, such as a control bar, movable along a path in which the coupling portions of control portions in one of the control positions are located.

in this manner, the respective latches are advanced by the reciprocating control bar to cooperate with the hooks which are reciprocated by the first operating means. The latches, whose coupling and control portions are in the other control position, remain unmoved. ln the preferred embodiment of the invention, the control position of the coupling portion located in the path of movement of the control bar, is the untensioned position, so that each control portion moves to this untensioned control position when the respective electromagnet is deenergized in accordance with the program.

In one embodiment of the invention, two control bars are arranged above each other for reciprocation, and cooperate with a single coupling portion of each latch. The upper control bar is used for closing the needle hook by the latch in the uppermost position of the knitting needle, and the lower control bar is used for closing the needle hook by the latch in the intermediate knock-over position of the latch needle. A switch controls each electromagnet, and is actuated when the upper control bar has passed the coupling portion in the inoperative tensioned control position. The switch de-energizes the respective electromagnet so that the respective control portion moves resiliently to the untensioned position where it is engaged by the lower control bar which moves the latch only to the knockover position.

In another embodiment of the invention, each control portion has two spaced coupling portions cooperating with a single control bar. When the control bar engages the lower coupling portion, the respective latch is moved to the uppermost position, but when the control portion of the latch, and the lower coupling means are held in the inoperative position by an energized electromagnet, the lower coupling portion is passed by the control bar which operates a switch so that the electromagnet is de-energized, and the control portion of the latch can resiliently move to the untensioned position in which the higher coupling portion is located in the path of movement of the single control bar which effects movement of the latch to the knock-over position. Due to the fact that resilient extensions of the latches are used as armatures of the selecting electromagnets, the apparatus is very simple as compared with prior art apparatus in which between the electromagnets and the latch extensions, two intermediate links are additionally interposed, namely an armature and an elastic needle. Moreover, the attraction of the armature control portions by the respective electromagnet, is automatic and does not require an auxiliary device. This is due to the fact that in order to disengage the coupling portion of the latch extension from the control bar in the lowest position of the latch, the end portion of the respective latch extension is provided with an end portion having a continuously downward extending profile, with a downward slanted upper face located in the path of movement of the lower edge of the control bar so that in the lowest position of the latches, the same are urged by the control bar to move to the tensioned position.

The coupling portion, or coupling portions, of the latches are formed in the same way, and are engaged by a stationary knock-over bar in the uppermost position of the latches so that the resilient latch extensions are pressed to the tensioned position in which they are held by the respective electromagnets.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view, partially in side section illustrating a first embodiment of the invention;

FIGS. 2, 3 and 4 are fragmentary side views, partially in section, corresponding to FIG. 1 but illustrating the apparatus in different operational positions;

FIG. is a fragmentary schematic rear view illustrating the selecting magnets shown in FIGS. 1 to 4; and

FIG. 6 is a side view, partially in section, illustrating a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to the embodiment of FIGS. 1 to S, and particularly to FIG. 1, the apparatus is shown in the lowest position of the hook part 1 of a latch needle which has a latch part 12 slidable in a tubular or slotted portion of the respective hook part 1. A row of latch needles 1, 12 is provided, only one being shown for the sake of simplicity.

The hook parts 1 are mounted in a holder 2 which is secured by a screw 3 to a needle bed 4 secured by screws 5 to a swinging arm 6 which is turnable about a shaft 6a between angular positions in which hook parts I move between the uppermost position shown in FIG. 2, and a lowermost position shown in FIG. 4. Pivot means 7a and 7b and a link 7, connect the swinging arm 6 with a swinging cam follower lever 8 having a cam follower roller 9, and being turnable about a shaft 8a. Cam follower roller 9 cooperates with a cam 10 on a driven shaft 1 1, which also controls a cam 29 cooperating with a cam follower roller 28 on a cam follower lever 27 also mounted for angular movement on shaft 8a. An articulated link 26 has pivots 26a and 26b connecting a control means 24 with the cam follower lever 27, so that during rotation of drive shaft 11, control means 24 is reciprocated in an up-and-down movement while being guided in a corresponding guideway of a stationary support 25 having a plate portion 25a. Con trol means 24 includes a control member 20 fixed by a screw 23, and having an upper control bar 20a and a lower control bar 20b which are parallel to each other and spaced in vertical direction. It is apparent that during rotation of drive shaft 1 1, control bars 20a, 2% will move up and down in synchronism with the up-anddown movements of the hook parts 1 since the first operating means 2 to 10, and the second operating means 20, 23 to 29, are both driven by the common drive shaft 1 1.

Each latch 12 has a butt portion 13 located under the lower end of the tubular hook part 1. Below the butt portions 13, latches 12 have resilient extensions 14 including portions 14a guided in slots of a stationary guide bar 15 which is fixedly secured to the stationary support 16 of a knock-over bar 16a.

Each extension 14 has a control portion 141: which forms an armature for a correlated electromagnet 17.

As best seen in FIG. 5, electromagnets 17 are narrow, and arranged in two parallel rows staggered to each other so that the spaces between adjacent extensions 14, and armature control portions 14b are fully utilized. The lines of symmetry of electromagnets 17 are spaced the same distance as the latches l2 and extensions 14. The two rows of electromagnets 17 are mounted in grooves in a holder 18.

The extensions 14 of each latch 1 are resilient, and tend to assume an untensioned control position spaced from the respective electromagnet 17, as shown in FIG. 3. When an electromagnet 17 is energized in a conventional manner by switches operated in accordance with a program, the respective control portion 14b, forming the armature of the electromagnet 17, is attracted to the tensioned control position shown in FIG. 2, in which the control portion 14b is closely adjacent the respective electromagnet 17. When an electromagnet 17 is de-energized in a conventional manner by a switch operated under the control of the program, or by a switch actuated by control means 24, 20, control portion 14b moves resiliently to the untensioned operative position.

Each control portion 14b has a coupling portion 19 which is formed with a downwardly slanted top face 190, and with a transverse bottom coupling face 19b. Each control portion 14b has a lower end portion 21 having a downwardly slanted face, and a transverse bottom face. The slanted face 190, and the slanted face of end portion 21 extend continuously downward.

In the position of FIG. 1, coupling portion 19 is inoperative, and end portion 21 is held by the lower control bar 20b in the tensioned control position. During the preceding downward movement of control bar 20b,

the slanted top face of end portion 21 was engaged by the lower edge of control bar 20b so that the resilient control portion 14b was pressed out of the untensioned control position to the tensioned control position shown in FIG. 1.

The slanted face 19a of coupling portion 19 cooperates with a stationary bar 22 mounted on the support 16 of the knock-over bar. If the resilient extension 14 is in the untensioned control position, and moves to the position of FIG. 2, the slanted top face 19a engages the stationary bar 22 so that extension 14 is pushed to the tensioned control position, and finally assumes the position shown in FIG. 2 in which resilient extension 14 is held in the tensioned position, irrespective of whether electromagnet 17 thereof is energized or not.

In the embodiment of FIGS. 1 to 4, two control bars 20a, 20b cooperate with one coupling portion 19.

In the embodiment of FIG. 6, a single control bar 20 is reciprocated, and cooperates with two coupling portions 19 on each extension 14. Otherwise, the construction of the embodiment of FIG. 6 is the same as shown in FIG. 1. Lapping guides 30 are arranged above the latch needles 1, l2 and designed and operated in a conventional manner for inserting warp threads 31 into the hooks 1 of the latch needles which knit a fabric 32.

The apparatus shown in FIGS. 1 to 4, and 5, operates as follows:

In the position of FIG. 1, the swinging arm 6 and the swinging arm 27 are in the lowermost dead center positions. The latch needles 1, 12 are in the lowest position, hooks 1 closed by latches 12, fabric 32 is suspended on stitches in latch needles 1, 12. The resilient control portions 14a of the latch extensions 14 are held in the tensioned control position adjacent electromagnets 17 by the lower control bar 20b after downward movement of the same during which the lower edge of control bar 20b sliding on the slanted face of end portion 21, pushed the end portion 21 to the illustrated position.

In the position shown in FIG. 1 coupling portion 19 is inoperative, and not located in the path of movement of control bar 200.

Due to the rotation of cam 10, the needle bed 4 is raised, and hook parts 1 are moved from the lowermost position to the uppermost position shown in FIG. 2. The simultaneous rotation of cam 29 causes rising of control means 24 with control bars 200 and 2012. It is assumed that some of the selecting electromagnets 17 are energized in accordance with a program, and the others remain de-energized.

When the lower lifting bar 20b is raised above end portion 21, the resilient extensions 14 cooperating with de-energized electromagnets l7 resiliently move from the tensioned initial control position to the untensioned control position in which the transverse bottom face 19b of coupling portion 19 is located in the path of movement of control bar 20a so that the respective latches 12 are raised to the highest position, corresponding to the highest position of the respective hook parts 1. Near the end of the upward movement of latch 12 and extension 14, the respective coupling portion 19 abuts with its slanted top face on the stationary bar 22, and is resiliently displaced toward the tensioned position until disengaged from the control bar 200. Thereupon, the point of coupling portion 19 engages the stationary bar 22, and the resilient extension 14 is held in the tensioned position close to electromagnet 17, as shown in FIG. 2.

At this moment, the needle hook 1 reaches its uppermost position, and is closed by latch 12 in the uppermost position so that during the following lapping operation, no thread can be inserted into the closed needle hooks so that in this phase, the latch needles 1, 12 whose correlated electromagnet 17 were selectively de-energized, do not carry out a knitting operation.

As regards the electromagnets energized in accordance with the program, by which some extensions 14 were held in the tensioned control position shown in FIG. 1 after release of the end portion 21 by the lower control bar 20b, there are two possibilities. Either switches energizing the electromagnet 17 are interrupted when the upper control bar 200 rises above coupling portion 19 of extension 14 so that the extensions l4 resiliently return to the untensioned operative position in which the respective coupling portions are engaged by the lower control bar 20b, as shown in FIG. 3, or electromagnet 17 remain energized during the en tire upward stroke of the control means 20, 24.

In the first case, as shown in FIG. 3, the respective latches 12 are raised to a knock-over position, and stopped in this position due to the fact that the lower control bar 20b engages coupling portion 19. The latch 12 remains in the knock-over position until hook 1 reaches the knock-over position, moving downward after insertion of a new thread into hook I in the uppermost position of hook I. When hook 1 reaches with the new thread the knock-over position, it is closed by the latch 12 held in this position by the lower control bar 20b. In the knock-over position, the stitch formed in the preceding phase, is knocked over from the needle 1, 12, forming a new stitch of a newly fed thread.

At the moment in which the upper control bar 200 has passed the coupling portion 19 of the control portion 14b held by electromagnet 17, a switch is operated by control means 24, 20 for disconnecting and de-energizing the respective electromagnet 17, so that the resilient extension 14 is free to resiliently move to the untensioned position shown in FIG. 3 in which the bottom face of coupling portion 19 is located in the path of movement of the lower control bar 20b, as shown in FIG. 3. Since control bar 20b is lower than control bar 200, the highest position of coupling portion 19 is lower than in the position of FIG. 2 in which the upper control bar 22a cooperates with coupling portion 19. Consequently, the knock-over position of latch 12 is lower than the highest position of latch 12 shown in FIG. 2.

When some electromagnets 17 remain energized during the entire upward stroke of control means 24, 20, as shown in FIG. 4, the extensions 14 are in the inoperative tensioned position in which coupling portion 19 is located outward of the path of movement of the rising control bars 200 and 20b. Latch 12 remains in the lowest position, and is closed by hook I after the same has moved up to the highest position shown in FIG. 2, and down to the lowest position shown in FIGS. 1 and 4. In the intermediate knock-over position of hook I, hook I is open so that the stitch formed in the preceding phase is not knocked over, and remains in hook I so that a blind loop is formed of the thread inserted into hook I in the highest position.

During the downward and rearward movement of needle bed 4, hooks 1 engage the butts 13 of the latches 12 which were raised in accordance with FIGS. 2 and 3 to the highest position or to the knock-over position, and pull the respective latches l2 downward to the lowermost position shown in FIG. 1. During the downward stroke of the control means 24, 20, all resilient extensions 14 are moved toward the inoperative positions adjacent the respective correlated electromagnets l7, partly by the action of the downward moving upper control bar 200 on the slanted top faces of coupling portions 19, partly by the action of the lower control bar b on the slanted top face of the end portion 21.

The operation of the embodiment of H6. 6 is similar to the operation described with reference to the embodiment of FIGS. 1 to 4, but a single control bar 20 cooperates with two coupling portions 19. When control bar 20 rises above the end portion 21, the respective extensions 14 adjacent the de-energized electromagnets 17 move to the untensioned control position in which the transverse bottom face of the lower coupling portion 19 is located in the path of movement of the rising control bar 20 so that the respective latch 12 is raised to the highest position, shown in FIG. 2, in which the closed hook I does not perform a knitting operation. Other selecting electromagnets 17, which are energized with the program hold the resilient extensions 14 in the inoperative position until control bar 20 has moved to a height located between the two coupling portions 19 where the control means 24, 20 actuate a switch to de-energize the respective selector electromagnet 17, so that the resilient extensions 14 move away from electromagnet 17 to the untensioned operative position in which the transverse face of the upper coupling portion is located in the path of movement of control bar 20 so that the rising control bar 20 moves extension 14 with latch 12 to the knock-over position where it is joined by the downward moving hook I so that a knitting operation is carried out by the respective latch needle. Electromagnet 17 held in the energized condition, hold the respective extensions 19 in the tensioned inoperative position, so that control bar 20 cannot engage the same while rising so that the respective latches 12 remain in the lowest position at which the hooks 1 also arrive after moving in an upward stroke and in a downward stroke.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of apparatus for controlling warp knitting latch needles differing from the types described above.

While the invention has been illustrated and described as embodied in a warp knitting apparatus having latch needles provided with resilient extensions forming armatures for selector magnets, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. Apparatus for controlling warp knitting latch needles, comprising, a set of electromagnets selectively energizable in accordance with a program; a set of latch needle means, each including a hook, and a latch including a resilient control portion having at least one coupling portion, said resilient control portions forming the armatures of said electromagnets, respectively, and being movable by the same between an untensioned control position, and a tensioned control position attracted by the respective electromagnet; first operating means for advancing and retracting said hooks; and second operating means including at least one reciprocating control means movable along a path in which said coupling portions of said control portions in one of said control positions are located so that the respective latches are advanced by said control means to cooperate with said hooks while the latches whose coupling and control portions are in the other control position remain unmoved.

2 Apparatus as claimed in claim 1 wherein said control means of said second operating means includes at least one control bar; and wherein said coupling portions are teeth located in said one control position in the path of said control bar.

3. Apparatus as claimed in claim 1 wherein said needles and latches are movable between uppermost positions and lowermost positions through knock-over positions; wherein said control means includes an upper control bar cooperating with said coupling portions in said one control position for moving selected latches to said uppermost positions for closing the respective hooks, and a lower control bar cooperating with said coupling portions in said one control position for moving other selected latches to said knockover positions for closing the respective hooks.

4. Apparatus as claimed in claim 3 including a switch controlling each electromagnet and being actuated by said control means when said upper control bar has passed said coupling portion of a control portion in said other control position so that said control portion and coupling portion are moved to said one control position under the control of said electromagnets, and said coupling portion is engaged by said lower control bar for moving said latch to said knock-over position.

5. Apparatus as claimed in claim 1 wherein said needles and latches are movable between uppermost positions and lowermost positions through knock-over positions; wherein said control means include a single control bar; wherein each control portion has upper and lower coupling portions cooperating with said control bar so that said control bar engaging the lower coupling portions of selected latches moves the same to said uppermost position for closing the respective hooks, and engaging said upper coupling portions of other selected latches moves the same to said knockover positions for closing the respective hooks.

6. Apparatus as claimed in claim 5 including a switch controlling each electromagnet and being actuated by said control means when said control bar has passed said lower coupling portion of a control portion in said other control position so that said control portion and said upper coupling portion are moved under the con trol of the respective electromagnet to said one control position and engaged by said control bar for movement of said latch to said knock-over position.

'7. Apparatus as claimed in claim 1 wherein said one control position is said untensioned control position and said other control position is said tensioned control position so that said control means advance latches whose correlated electromagnets are de-energized in accordance with the program.

8. Apparatus as claimed in claim 7 wherein said control means includes at least one control bar; and wherein each coupling portion has a slanted face and a coupling face transverse to the direction of movement of said control bar so that during movement of said control bar in one direction said control bar engages said slanted face and urges said control portion to said tensioned control position, and so that during movement of said control bar in the opposite direction, said control bar engages said coupling face of said coupling means of a control portion in said untensioned control position.

9. Apparatus as claimed in claim 8 wherein each control portion has an end portion having a slanted face cooperating with said control bar so that at the end of movement in said one direction, said control bar engages said slanted face and urges said control portion to said tensioned position.

10. Apparatus as claimed in claim 8 comprising a stationary bar engaged by said slanted face of said coupling portion during movement to the highest position of said latch so that said coupling portion and control portion are pushed by said stationary bar to said tensioned control position with said transverse face sliding on said control bar, and are held in said tensioned control position in said highest position of said latch by said stationary bar.

l I I I 

1. Apparatus for controlling warp knitting latch needles, comprising, a set of electromagnets selectively energizable in accordance with a program; a set of latch needle means, each including a hook, and a latch including a resilient control portion having at least one coupling portion, said resilient control portions forming the armatures of said electromagnets, respectively, and being movable by the same between an untensioned control position, and a tensioned control position attracted by the respective electromagnet; first operating means for advancing and retracting said hooks; and second operating means including at least one reciprocating control means movable along a path in which said coupling portions of said control portions in one of said control positions are located so that the respective latches are advanced by said control means to cooperate with said hooks while the latches whose coupling and control portions are in the other control position remain unmoved.
 2. Apparatus as claimed in claim 1 wherein said control means of said second operating means includes at least one control bar; and wherein said coupling portions are teeth located in said one control position in the path of said control bar.
 3. Apparatus as claimed in claim 1 wherein said needles and latches are movable between uppermost positions and lowermost positions through knock-over positions; wherein said control means includes an upper control bar cooperating with said coupling portions in said one control position for moving selected latches to said uppermost positions for closing the respective hooks, and a lower control bar cooperating with said coupling portions in said one control position for moving other selected latches to said knockover positions for closing the respective hooks.
 4. Apparatus as claimed in claim 3 including a switch controlling each electromagnet and being actuated by said control means when said upper control bar has passed said coupling portion of a control portion in said other control position so that said control portion and coupling portion are moved to said one control position under the control of said electromagnets, and said coupling portion is engaged by said lower control bar for moving said latch to said knock-over position.
 5. Apparatus as claimed in claim 1 wherein said needles and latches are movable between uppermost positions and lowermost positions through knock-over positions; wherein said control means include a single control bar; wherein each control portion has upper and lower coupling portions cooperating with said control bar so that said control bar engaging the lower coupling portions of selected latches moves the same to said uppermost position for closing the respective hooks, and engaging said upper coupling portions of other selected latches moves the same to said knock-over positions for closing the respective hooks.
 6. Apparatus as claimed in claim 5 including a switch controlling each electromagnet and being acTuated by said control means when said control bar has passed said lower coupling portion of a control portion in said other control position so that said control portion and said upper coupling portion are moved under the control of the respective electromagnet to said one control position and engaged by said control bar for movement of said latch to said knock-over position.
 7. Apparatus as claimed in claim 1 wherein said one control position is said untensioned control position and said other control position is said tensioned control position so that said control means advance latches whose correlated electromagnets are de-energized in accordance with the program.
 8. Apparatus as claimed in claim 7 wherein said control means includes at least one control bar; and wherein each coupling portion has a slanted face and a coupling face transverse to the direction of movement of said control bar so that during movement of said control bar in one direction said control bar engages said slanted face and urges said control portion to said tensioned control position, and so that during movement of said control bar in the opposite direction, said control bar engages said coupling face of said coupling means of a control portion in said untensioned control position.
 9. Apparatus as claimed in claim 8 wherein each control portion has an end portion having a slanted face cooperating with said control bar so that at the end of movement in said one direction, said control bar engages said slanted face and urges said control portion to said tensioned position.
 10. Apparatus as claimed in claim 8 comprising a stationary bar engaged by said slanted face of said coupling portion during movement to the highest position of said latch so that said coupling portion and control portion are pushed by said stationary bar to said tensioned control position with said transverse face sliding on said control bar, and are held in said tensioned control position in said highest position of said latch by said stationary bar. 